The present invention relates to a drive device and more particularly relates to a drive device having a rotary motor and a reduction device which connects the motor to the object to be driven while tolerating considerable shaft angular and radial misalignments between the object to be driven and the drive device.
In a wide variety of applications in which precise control of the amount of rotation of a rotary device is important, it is imperative that the output of a motor be precisely reduced and transferred to the input of the rotary device. For example, the rotation of siderostat mirrors must be precisely controlled through extremely small increments to allow the mirrors to track celestial objects. Worm and worm wheel drives are typically used to drive the mirrors. However, precise control of the rotation of such mirrors or of any relatively large object is difficult, since rotation of such devices tends to produce backlash which reduces the precision of the drives.
Spring loaded devices have been provided in some of these previously-known drives to remove the backlash resulting from the rotation of the driven objects. While these spring-loaded devices help prevent backlash, they have the disadvantage of accelerating wear of the teeth of the worm gears by increasing the contact forces between the gears. In addition, these anti-backlash devices limit the rotational stiffness of the device. Such a reduction of stiffness decreases the precision of a drive since the mirror is relatively heavy.
In addition, worm wheel drives are often incapable of providing sufficient gear reduction. Those devices which do employ multiple reduction devices to provide the required degree of reduction tend to be relatively large. This can be disadvantageous in applications in which the drive devices must be positioned in relatively small spaces.
Another problem present in systems using worm wheel drives is the inability of the drives to provide the degree of reduction needed to provide for very small rotations of the mirror while still minimizing backlash and maximizing stiffness.
All of these problems are compounded if the object to be driven is radially or axially misaligned with the drive device, since such a misalignment may give rise to axial or radial forces that may hamper the operation of the device or even damage the device. Of course, the problems associated with such reduction devices are not limited to drives for siderostat mirrors, but also arise in any application where precise control of the rotation of an object is important.